As of Aug. 1, 1989, there were U.S. Pat. No. 102,621 cases of acquired immunodeficiency syndrome (AIDS) in the United States as reported to the Centers for Disease Control (CDC) (published data, "Statistics from the World Health Organization and The Centers for Disease Control," AIDS, Oct. 1989, 3(10):677-681. This is almost double the number reported as of Jan. 6, 1988 (51,916) (published data, "Statistics from the World Health Organization and The Centers for Disease Control," AIDS, 2(1):65-69). The alarming increase of AIDS cases has increased the attention given to barrier devices such as condoms. The U.S. Public Health Service has strongly advised the use of condoms to combat the sexual transmission of this deadly disease for those who neither practice abstinence nor maintain a faithful monogamous relationship (brochure, "Understanding AIDS," HHS Publication No. (CDC)HHS-888404, U.S. Government Printing Office, 1988). Although the use of condoms will not assure absolute safety of the user against the transmission of viral disease, it is expected to reduce the risk of transmission. This expectation, however, is based on mostly qualitative evaluations.
Epidemiologic studies on the use of condoms as prophylactics suggest that condoms can be effective. D. Barlow, "The condom and gonorrhea," Lancet, 15 Oct. 1977, 2(8042):811-812, found that those who reported used condoms "correctly" (consistently) were at a lower risk of contracting bacterial transmitted gonorrhea than those who reported used condoms "incorrectly" (inconsistent use or some unprotected genital contact). Furthermore, the group of "incorrect" users was not statistically better off than the group who did not use condoms at all. Still, about 4% of the subjects who used condoms correctly contracted gonorrhea.
Fischl et al, "Evaluation of heterosexual partners, children, and household contacts of adults with AIDS," JAMA, 6 Feb. 1987, 257(5):640-644, conducted a study where human immunodeficiency virus (HIV) seropositive patients and their HIV seronegative partners were monitored for 1-3 years after diagnosis. They found that only 1 of 10 partners who were sexually active and used condoms seroconverted whereas, 12 of 14 who were sexually active and did not use condoms seroconverted. Also, 0 of 8 seroconverted who remained abstinent. From these studies, the source of the failure to prevent transmission of STDs when condoms were used is difficult to assess.
The quality control protocol used by manufacturers to screen condoms, which was established by the American Society for Testing and Materials (ASTM), calls for filling the condom with 300 ml of water, suspending the condom, and inspecting the surface for leakage (see ASTM, D 3492-83). The test is designed for rapid testing of large numbers of condoms. A lot of condoms is rejected if the number of samples that fail the test meets or exceeds the rejection number associated with an Acceptable Quality Level (AQL) of 0.4% (see MIL-STD-105D). The Food and Drug Administration (FDA) routinely inspects manufacturers to assure that this level of quality continues, using a similar water fill test which also provides for rapid bulk testing. Neither the ASTM nor the FDA test protocols, however, are very similar to the physiologic situation. The geometry of expansion when 300 ml of water is poured into the condom, for example, is not very similar to physiologic expansion.
A number of studies using a basic experimental design with a simple plunger to simulate sexual intercourse have been designed to qualitatively model physiologic conditions. Katznelson et al, "Efficacy of the condom as a barrier to the transmission of cytomegalovirus," J. Infect Dis., July 1984, 150(1):155-157, working with cytomegalovirus (CMV), in a static experiment, found that no transmission was detected from 12 latex condoms incubated at 37.degree. C. for 15, 30, and 60 minutes with 2 ml of virus suspension. Five condoms sampled after 30 minutes of simulated sexual intercourse showed no transmission of CMV.
Conant et al, "Herpes simplex virus transmission: Condom studies," Sex Transm. Dis., Apr-Jun 1984, 11:94-95, working with herpes simplex virus type-2 (HSV-2), found that, when condoms were placed on a syringe plunger with 4 ml of virus suspension inside, and then "pushed up and down forcefully 50 times" in the syringe barrel, no transmission was detected through the one latex and the one natural membrane condoms tested. In a more recent study using a similar experimental design, Conant, working With HIV and a mouse retrovirus, reported no transmission through three latex and two natural membrane condoms (Conant et al, "Condoms prevent transmission of AIDS-associated retrovirus," JAMA, 4 April 1986, 255(13):1706.
Van De Perre et al, "The latex condom, an efficient barrier against sexual transmission of AIDS-related viruses," AIDS, May 1987, 1(1):49-57, using a modified Conant model with 3 ml HIV suspension, at 37.degree. C., found transmission after 60 minutes in 0 of 10 latex condoms, and in 1 of 2 natural membrane condoms.
Rietmeijer et al, "Condoms as physical and chemical barriers against human immunodeficiency virus," JAMA, 25 March 1988, 259(12):1851-1853, also working with HIV, but using an ethylene oxide-sterile form and a graduated cylinder for plunger and receptacle respectively, found no transmission in 10 latex condoms.
Judson et al, "In vitro evaluation of condoms with and without nonoxynol 9 as physical and chemical barriers against chlamydia trachomatis, herpes simplex virus type 2, and human immunodeficiency virus," Sexually Transmitted Diseases, Apr.-June 1989, 16(2):51-56, working with chlamydia trachomatis, HSV-2, and HIV, using the setup of Rietmeijer, found no transmission of chlamydia for 50 latex condoms. No transmission of HSV-2 or HIV was detected for 10 latex condoms.
While these studies support the assessment that condoms reduce the risk of transmission, the small sample size and the nonphysiologic character of the models used, makes a realistic quantitative assessment of condom efficacy as a barrier in the physiologic environment impossible. In addition, these studies and others like them lack any positive controls which would demonstrate the ability of the test to detect leakage.
Minuk et al, working with hepatitis B virus (HBV), hepatitis B surface antigen (HBsAg), herpes simplex virus (HSV) and CMV, using a vibration design instead of the plunger, found no transmission of any viral probe through 15 latex condoms tested with each of these probes. However, the smallest probes, HBSAg (22 nm) and HBV (42 nm), passed through three natural membrane condoms still, some important conditions during intercourse are only qualitatively simulated by the vibrator. When such test methods are used to interpret the value of added measures of protection such as nonoxynol-9, as was done in the studies by Rietmeijer and Judson, assessment of the added benefit can only be qualitative.
Lytle et al, working with .phi.X174 and HSV in a study of natural membrane condoms only, using a beaker and a mixing bar for agitation, found that 12 of 26 natural membrane condoms leaked the smaller .phi.X174 virus (27 nm diameter). Also, when a mixture of .phi.X174 and HSV (150 nm diameter) was used, 2 natural membrane condoms which did leak .phi.X174 did not leak HSV. The study indicated that leakage of a small virus does not necessarily indicate leakage of a larger virus and that leakage rates through natural membranes were quite variable.
The present invention is an improvement over prior methods utilized for testing condoms, which quantifies physiologic conditions. Moreover, the present invention provides a method of evaluating the permeability of a variety of membrane articles.